German patent application DE 10 2005 019 356 A1 discloses a method for joining a turbine blade to a rotor base during the production or repair of a gas turbine rotor with integrated blades by means of friction welding. In friction welding, components are fused together by friction and integrally joined to each other. In linear friction welding, one component is moved back and forth translatorily, while the other component is stationary and it is pressed with a certain amount of force against the moving component. In this process, the mating faces of the components that are to be joined together adapt to each other as a result of hot forging. The method described in the state of the art entails the two components that are to be joined or fused to each other, that is to say, the rotor base and the turbine blades as well as another mating part as an adapter element. The two components that are to be joined and the adapter element are oriented with respect to each other in such a way that the adapter element is arranged as an insert between the two components. In order to join the components, the adapter element is moved relative to the two components, a process in which an upset force is exerted via the stationary components onto the joining zones between the components and the adapter element.
By means of the described method, a gas turbine rotor with integrated blades can be produced in the form of a blisk or bling relatively easily. However, the components to be joined and the adapter element have to be made of the same material. If the rotor base and the turbine blades are made of a titanium-based alloy, the adapter element employed is likewise made of a titanium-based alloy.
Up until now, it has not been possible to create a hybrid or graduated blisk design for a gas turbine rotor in which the rotor base is made of a high temperature-resistant nickel alloy such as, for instance, Inconel 718, while the turbine blades are made of a TiAl alloy since, at the working temperature of about 650° C. [1202° F.], the material used for the blades, especially the aluminum, diffuses into the joining zone or into the material used for the rotor base. This changes the chemical composition of the rotor base and of the turbine blades in the joining zone in such a way as to form a new material state with new phases. This phase formation, however, reduces the reliability and service life of the joining zone. The durability of the component joint is also detrimentally affected by the different thermal expansion of the materials.